Saving public files in the internal storage

问题:

I have an application that saves files downloaded from a server. These files are not private to my application and should be accessible to other applications as well. I want to know what would be the correct path to save these files when the SD card is ABSENT. For the SD card, there is the well known API -

getExternalStorageDirectory()

For the application's private data in the internal memory there is -

Context.getFilesDir()

On some devices, the internal memory is represented by /emmc/.

It will be really helpful if someone could elaborate on /emmc/. I know it stands for embedded Memory card and is not present in all the devices. But is it really representative of the internal memory? Or is it the third memory?

Should I save the files using openFileOutput() with MODE_WORLD_READABLE?

回答1:

On some devices, the internal memory is represented by /emmc/.

/emmc/ may exist on some devices, and it may be internal, but it may not be accessible to applications, and it certainly is not part of the Android SDK unless that happens to be what getExternalStorageDirectory() returns.

But is it really representative of the internal memory?

No.

Or is it the third memory?

Ask your device manufacturer.

Should I save the files using openFileOutput() with MODE_WORLD_READABLE ?

That is impossible to answer in the abstract. You say that your files "should be accessible to other applications as well", but you have not indicated why you expect any other application to care one bit about your files. Other applications will not be scanning your directories for files -- at best, they will allow users to browse external storage. The only reason to have a file that is MODE_WORLD_READABLE is if your application will be triggering another application to do something with the file (e.g., ACTION_VIEW Intent).

回答2:

I realize this is old and has an accepted answer, but I think the question is still relevant and that there is a way to achieve what the asker wants.

To paraphrase, I believe the asker wants to save a file, and make it accessible (e.g. for viewing) by other apps, without having to think about external storage (e.g. an additional permission and the possibility that the external storage is not present).

It turns out that you can make your own files readable by other apps.

File file = new File( ctx.getCacheDir(), "picture" );               
...
file.setReadable( true, false );
  // makes file readable to other apps

// Get another app to view my picture
Uri uri = Uri.fromFile(file);          
Intent intent = new Intent( Intent.ACTION_VIEW );
intent.setDataAndType( uri, "image/*" );
ctx.startActivity( intent );

The setReadable made the above code work for me - without that line the viewer app couldn't read the file. Note that setReadable operates on the whole directory, so the best solution is probably to create a sub-directory name 'public' and put your files in there.